Different types of dental plaque predispose to either caries or periodontal disease. Bacteria are intimately involved in both processes. Their role may be simply overgrowth in areas where hygiene cannot be maintained or certain bacteria may be etiologically responsible. The present proposal will examine both hypotheses as plaque will be removed from non-disease associated sites, from caries associated sites, from gingivitis associated sites and from subgingival sites associated with periodontitis. Pooling of plaque samples will be avoided so that the bacteriological and biochemical information obtained can be correlated with clinical appearance of the sampled site. The plaques will be 1) examined bacteriologically either by screening for certain bacteria or by partially characterizing the predominant culturable isolates; 2) compared in their physiologic response to certain radioactive nutrients such as sucrose and amino acids; 3) assayed for infectivity and chemotactic capability. Plaques removed from caries active sites have elevated levels of Strep. mutants and decreased levels of Strep. sanguis relative to non-caries associated sites. We will study the interactions between these two organisms in vitro in batch and continuous cultures. Meaningful differences between caries active and inactive plaques and between plaque associated with normal and periodontal conditions will be used in a clinical situation to determine whether they will be of any value in identifying a disease process before tissue destruction is clinically evident.